bacillus

Etymology

It is borrowed from New Latin bacillus,^[2][3][4] from Late Latin bacillus (“little rod, wand”),^[5][6][4][7] found in Isidore,^[5] a diminutive of Latin baculum (“stick, staff”) or its variant baculus.^[5][8][9] Barnhart takes it as a variant of the older diminutive bacillum (“small stick”),^[3][10][11] and Merriam-Webster Unabridged as a Medieval Latin alteration of the noun for a stick.^[2] Barnhart also thinks the scientific use was prompted by French bacille, recorded in 1842.^[3] The Latin noun has cognates in Ancient Greek βακτήριον (baktḗrion, “small staff”) and βάκτρον (báktron, “stick, staff”).^[3][11] Etymonline and the American Heritage Dictionary derive it from Proto-Indo-European *bak- (“staff”),^[4][6][3] but de Vaan notes that b was very rare in Proto-Indo-European and that the Celtic forms are irregular, so a loanword is the likelier explanation.^[11]

Earliest recorded meaning

The genus of rod-shaped bacteria: Merriam-Webster Unabridged gives 1868 as its first known use.^[2] Etymonline dates the word to 1877,^[4] Dictionary.com to 1880–85,^[10] and the OED and Barnhart first record it in English in 1883, in an article by H. J. Slack in Knowledge.^[5][3]

Semantic evolution

The botanist Ferdinand Cohn had introduced the word as a term of bacteriology in 1853.^[4][8] The OED's entry still describes a genus of microscopic organisms split off from Bacterium.^[5] The name also covers any rod-shaped bacterium,^[4][9][2] and loosely any bacterium that causes disease.^[9][2]

Timeline

• 1868 – the genus of rod-shaped bacteria.^[2] The OED and Barnhart first record the word in 1883.^[5][3]
• 1877 – any rod-shaped bacterium.^[4]

Meanings

Noun

1. Any bacterium of the genus Bacillus, rod-shaped and usually aerobic, which forms endospores and includes the cause of anthrax.^[2][12][13]
2. Any rod-shaped bacterium, as opposed to a coccus or spirillum.^[2][12][13]
3. Loosely, any bacterium, especially one that causes disease.^[2][9]

Word family

• thiobacillus
• Actinobacillus
• comma bacillus
• bacillary

Related words

• bacterium
• bacteria
• debacle
• imbecile
• baguette

Usage notes

The plural is bacilli.^[2][12][9] Merriam-Webster Unabridged also enters a capitalized Bacillus as a genus of stick insects, with the same origin in the Medieval Latin for "small staff" and a first known use of 1810.^[2]

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
3. ^ a b c d e f g Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
4. ^ a b c d e f g Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
5. ^ a b c d e f Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
6. ^ a b The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
7. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
8. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
9. ^ a b c d e Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
10. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
11. ^ a b c de Vaan, Michiel (2008), Etymological Dictionary of Latin and the other Italic Languages, Leiden Indo-European Etymological Dictionary Series 7, Leiden; Boston: Brill
12. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins
13. ^ a b Stedman's Medical Dictionary, Baltimore: Lippincott Williams & Wilkins